If you would like to have an instance stopped so you are no longer billed but would still like to keep the instance on hand to bring back up again, you will need to create a snapshot and terminate the instance.

From your Cloud Dashboard, when viewing your instances go to actions on the right, and click on create a snapshot.  This creates a full snapshot of your instance.  Once this is completed you can use this snapshot to launch a new instance at any time.

Now, terminate the instance.  You will need to terminate instances, as even if an instance is in a paused or shut down state, it has its resources allocated and dedicated to it.  The only way to free these resources and to not be charged is to terminate instances.

Pausing or suspending the instance simply puts that instance on hold, either in RAM (paused) which is quicker, or on disk (suspend) which is slower. The resources are still dedicated to that VM in those states.